bronchoconstrictor

Bronchoconstrictor is a substance or process that causes narrowing of the airways by constricting the smooth muscle in the bronchial walls. In medical use, the term often refers to endogenous mediators released during allergic or inflammatory reactions, or to pharmacologic agents that provoke bronchoconstriction in diagnostic tests.

Key endogenous bronchoconstrictors include acetylcholine released from parasympathetic nerves, histamine released from mast cells, and cysteinyl leukotrienes (LTC4, LTD4, LTE4). Other mediators such as prostaglandin D2 and certain tachykinins can contribute. Bronchoconstriction results from contraction of airway smooth muscle, increased mucus secretion, and, in susceptible individuals, airway edema. The response is a central feature of asthma and is increased in airway hyperreactivity. Triggers include allergens, cold air, exercise, and irritants.

Methacholine and carbachol are cholinergic agents used in diagnostic bronchial challenge tests to quantify airway hyperresponsiveness; these substances act as bronchoconstrictors. Clinically, bronchoconstriction is countered with bronchodilators such as beta-adrenergic agonists and anticholinergic agents, and with anti-inflammatory treatments that reduce mediator release. Understanding bronchoconstrictors is important in managing asthma, allergic rhinitis with bronchial involvement, and chronic obstructive pulmonary disease in cases with bronchospasm.